1. Field of Invention
This invention relates in general to the display of objects in an interactive information handling system and in particular to a method for automatically selecting the size of an object to be displayed in a "window" on the display in accordance with the size of the window.
2. Description of the Related Art
The prior art discloses various interactive information handling systems. A personal computer, comprising a systems unit, a display device and a keyboard is an example of a simple interactive information handling system. Personal computers are capable of displaying various types of data objects such as text, business graphic objects such as flow charts, pie charts etc, and more complex graphic objects such as two and three dimensional drawings and pictures. The type of objects that may be displayed by a personal computer depends primarily on the display device per se, the adapter board that is controlling the display, and the application program that is run on the system. An article entitled "The IBM Color/Graphics Adapter" by T. V. Hoffmann, beginning on page 26 of the PC Tech Journal, Vol. 1, No. 1, dated July/August, 1983 provides an understanding of some of the general technology considerations that are involved in displaying information in a personal computer system and a detailed understanding of the operation of the IBM color graphics adapter and display device.
In that article three types of display devices are discussed, the monochrome monitor, the color monitor, and a TV monitor. The article also discusses the various operating modes that display system can use in terms of resolution and sets forth some of the defacto standards that have been established in the industry. Some display systems are limited to displaying text in one color. In a typical monochrome system for displaying text, the screen has an 80 column, 25 line format. Each horizontal scan line consists of 720 picture elements, while there are 350 horizontal scan lines. The system is said to have a resolution of 720 by 350. Each of the character columns is 9 pels wide (720/80), while each line of text comprises 14 horizontal scan lines (350/25). A box for each character is therefore defined by a 9 pel by 14 pel area of the screen. Different display systems are available in the art with different resolutions and therefore different character box sizes.
The information that is displayed on the screen is resident in a video buffer that is normally located on the adapter card installed in the system unit. This buffer is continually scanned to refresh the information on the screen at a relatively high rate to avoid any flicker of the screen. The buffer normally includes at least one storage position for each pel on the display screen. The buffer is scanned, i.e. the bit positions addressed and clocked out in synchronization with the horizontal and vertical sweep signals of the display device. Text information e.g. characters and symbols are developed and transferred to the video buffer in at least two different ways. In the first technology, a bit mapped representation of each character in the character set is stored in a Read Only Memory (ROM) on a grid corresponding to the 9 by 14 character box of the display screen. Data entered into the system may be represented by two binary bytes, the first of which selects the particular character in ROM, and the second of which determines certain display attributes for the character such as underlining or blinking. The second general approach employed for developing charactersemploys "software character fonts" which are programs that function to draw the character on the 9 by 14 character box by programming statements. This later approach has the advantage that the character set font, i.e. the appearance of the character, may be changed merely by loading another program, and permits a number of character sets to be stored having different fonts. This is important in those applications which use screen images directly, such as making 35 mm slides for presentations.
The Hoffmann article also refers to the all points addressable (APA) types of display systems which are necessary to display graphics and generally also employ color. The software fonts are used also in the APA display technology and have the advantage of providing a number of different character sets employing different fonts and different sized character boxes on which the character sets are based. Selecting a different character set allows more columns and lines of text to be displayed on a given sized screen.
The prior art also discloses a display technique in which a "window" is created on the display screen which effectively overlays the information that was being displayed. The window area may be blank except for a cursor to indicate a position in the window where some editing action can occur or it may contain information such as a menu which allows the operator to run a completely different application within the window. The windowing display technique has been improved considerably in recent years to permit multiple windows to be created, to permit the location of the window to be moved dynamically from one position on the screen to another using "click and hold" mouse techniques, and to select the initial size of the window and also cause the window size to dynamically grow horizontally and vertically by similar "click and hold" mouse techniques.
A problem exists in prior art display systems which permit the size of the window to dynamically change when the window contains text and one or both of the window's dimensions are shortened. When, for example, the width of the window is changed from 40 columns to 30 columns, the text that was originally on the 40 character line can not fit on the 30 character line. One prior art solution attempts to solve the loss of data problem by "wrapping"the line around to the beginning of the next line. This is of course a limited solution since there may be text on all the lines displayed in the window so data on the last lines is lost. When the vertical dimension of the window is shortened, the problem is compounded since there is no way to provide a similar function as word wrapping. The problem is solved in some systems by letting the data "scroll" in either or both directions. The present invention is directed to an improved method for displaying information in the window of a display device in which the size of each displayed object is reduced in accordance with the reduction of the window so that all of the information that was originally displayed is maintained.